It was necessary to place the power supply elsewhere.
Apparently the previous position was critical. On the new position the hum is gone.
Somehow the PLL module seems to be sensitive to the magnetic fields of the transformer.
Strange, as it is shielded. its 12 Volt input is decoupled by several capacitors.
Well anyway this problem is solved. fortunately enough space was available in the 19 inch box.
I also wired the ON/OFF switch.
The transceiver is now usable but I don't want to connect it to a antenna yet.
First I need to check the harmonics and other spurious emissions.
Next thing to fix is the 10.7 MHz FM modulator.
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